MAGNETIC RECORDING HEAD HAVING CONSTANT-WIDTH RECORDING GAP SUBJECTED TO DECAYING AMPLITUDE BIAS

摘要

1,141,726. Electromagnetic printing. STANDARD TELEPHONES & CABLES Ltd. 2 June, 1967, No. 25608/67. Heading B6C. [Also in Division G5] Recordings are made on a magnetic medium by an effectively moving gap in a stationary recording head produced by applying to the head a gradually decaying A.C. bias signal to provide a flux which follows a path whose reluctance reduces gradually from one end of the head to the other. As shown, an offset bias winding 1 is arranged between saturable flanges 5 attached to polepieces 6, 7 so that the reluctance path reduces from end A to end G. The signal "winding" comprises a single wire 8 in a gap 16 and the materials of the polepieces and medium 9 are chosen so that the magnetic circuit between them has a rectangular hysteresis loop (Fig. 3). When the A.C. bias is applied in the absence of a record signal, successive regions across the head are demagnetized. When a record signal is present and when the bias amplitude at a particular region is just insufficient to take that region through a complete cycle and thereby change its state of magnetisation, that part of the record signal prevailing adds a relatively D.C. component to the bias so as to record that part of the signal 15 (Fig. 3) at that region, the amplitude ΠH1 of the record signal being insufficient by itself for recording. Transverse tracks may thus be recorded across a magnetic tape for video recording, the tape being driven either continuoulsy or stepwise, the signal being recorded while the tape is stationary. In either case, a sync. pulse is interposed between successive signals. In modified constructions, the signal winding 8 is disposed in a slot in one of the pole pieces (Figs. 4A, 4B, not shown), or in a separate core member on the opposite side of the tape from the biasing core (Figs. 6A, 6B, not shown), or a generally U-shaped core may have the winding 8 in one limb with the tape passing between the limbs (Figs. 5A, 5B, not shown). The head may be used in non-percussive printing in which a signal is recorded across the width of a drum or band, made visible with magnetic powder which is then transferred to a sheet under pressure, and finally "fixed" by heating.